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Slide Guide Used in Fluorescence Microscope

Thursday, 01 February 2007

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The CellTracks Analyzer II is a type of
epi-fluorescence microscope, where
observation of fluorescence are from
above (“epi”) the sample. Like a regular
microscope, a fluorescent microscope
produces a magnified image of the sample,
only the image emanates from fluorescence
of the subject, rather than from
the light originally used to illuminate the
sample. As a unit, CellTracks Analyzer II
consists of a dedicated computer loaded
with CellTracks software, mouse, and
keyboard. Immunicon uses a “systems”
approach to cancer detection. The
CellTracks included a tube developed to
preserve blood, presumably with CTC
cells, en route to a lab. The device contains
a system that standardizes and automates
sample preparation. Images of all
filters are compiled and presented in a
gallery format for final cell classification
by a lab technician on the computer. In a
typical epi-fluorescence microscope, the
illumination light (with regard to the
CellTrack Analyzer II, from a mercury
arc-discharge lamp) first filtered of
unnecessary wavelengths and bounced
off a dichroic mirror (a type of mirror
that reflects some wavelengths but allows
others to pass through it) to the sample.
Light coming from the sample passes
through the dichroic mirror again, and
is then separated further from the much
weaker emitted fluorescence via an emission
filter. The dichroic mirror is mounted
to the filter cube. The excitation and
emission filters are usually also affixed to
the filter cube.

In a typical protocol is as follows: a
blood sample is collected in the tube
and placed in a cartridge containing a
reaction chamber. The cartridge, with
the sample, is inserted into a cell presentation
device, a fixture of two magnets
held together by steel. Cells are then
subjected to magnetic nanoparticles,
called ferrofluids, that are conjugated to
antibodies that target rare cells including
CTCs. As part of the cell isolation
process, a separate device that is part of
the CellTracks system, called a MagNest,
magnetizes the sample. This causes the
targeted cells to become immuno-magnetically
labeled — targeted cells that
have the ferrofluids bound to them via
the antibodies collect in the magnetic
field. The magnetized cells are also
brought closer to the surface of the reaction
chamber, ready to be scanned. The
magnets are then retracted, the cells are
re-suspended, and staining reagents are
added. Staining (also called labeling),
involves target-specific, fluorescent dyes
called fluorophores. In the case of the
CellTracks Analyzer, three fluorophores
are used, one to color the nucleus of the
cell, another stains the cell membrane
and other non-nucleic structures, and
another colors specifically white blood
cells. Cancerous cells are identified
when they register with the first two
dyes, but not the third. The specimen is
then illuminated with light at a specific
wavelength that is absorbed by the fluorophores,
causing them to emit longer
wavelengths of light; a common fluorophore,
GFP, is harvested from jellyfish,
and fluoresces a characteristic bright
green when exposed to blue light. The
process is very specific, allowing doctors
to find a relatively small amount of targeted
cells, or even one, among several
billions of others.

More Information

For more information contact Larry Hansen of
NB Corp. of America at 1-800-521-2045; Frank
Modica, Manager of Mechanical Engineering
at Immunicon, at This email address is being protected from spambots. You need JavaScript enabled to view it.; or
visit http://info.hotims.com/10962-391.

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